Prepare handshake synchronization

Common
* Replace LocalDateTime with Instant everywhere

Client
* Display message creation date with system time zone in MessageControl
* LocalDB#users now strictly contains Users
* lastSync time stamp in LocalDB (saved per user)
* isOnline parameter in save function (lastSync updated if true)
* lastSync time stamp in LoginCredentials
* No ClientConfig#getLoginCredentials because of missing information,
  moved to LoginScene
* Pass LocalDB#lastSync to LoginCredentials in LoginScene

Server
* Explicit lastSync parameter for
  PersistenceManager#getPending(Group)Messages

This sends the correct time stamp to the server, however the JPQL
queries have yet to be adjusted.

client/src/main/java/envoy/client/data/ClientConfig.java

@@ -5,10 +5,8 @@ import static java.util.function.Function.identity;
 import java.io.File;
 import java.util.logging.Level;
 
-import envoy.client.ui.Startup;
 import envoy.data.Config;
 import envoy.data.ConfigItem;
-import envoy.data.LoginCredentials;
 
 /**
  * Implements a configuration specific to the Envoy Client with default values
@@ -105,11 +103,4 @@ public class ClientConfig extends Config {
 	 * @since Envoy Client v0.3-alpha
 	 */
 	public boolean hasLoginCredentials() { return getUser() != null && getPassword() != null; }
-
-	/**
-	 * @return login credentials for the specified user name and password, without
-	 *         the registration option
-	 * @since Envoy Client v0.3-alpha
-	 */
-	public LoginCredentials getLoginCredentials() { return new LoginCredentials(getUser(), getPassword(), false, Startup.VERSION); }
 }

client/src/main/java/envoy/client/data/GroupChat.java

@@ -1,7 +1,7 @@
 package envoy.client.data;
 
 import java.io.IOException;
-import java.time.LocalDateTime;
+import java.time.Instant;
 
 import envoy.client.net.WriteProxy;
 import envoy.data.Contact;
@@ -46,7 +46,7 @@ public class GroupChat extends Chat {
 				else {
 					gmsg.getMemberStatuses().replace(sender.getID(), MessageStatus.READ);
 					writeProxy
-						.writeMessageStatusChange(new GroupMessageStatusChange(gmsg.getID(), MessageStatus.READ, LocalDateTime.now(), sender.getID()));
+						.writeMessageStatusChange(new GroupMessageStatusChange(gmsg.getID(), MessageStatus.READ, Instant.now(), sender.getID()));
 				}
 			}
 		}

client/src/main/java/envoy/client/data/LocalDB.java

@@ -1,5 +1,6 @@
 package envoy.client.data;
 
+import java.time.Instant;
 import java.util.*;
 
 import envoy.data.*;
@@ -20,11 +21,12 @@ import envoy.event.NameChange;
  */
 public abstract class LocalDB {
 
-	protected User					user;
-	protected Map<String, Contact>	users		= new HashMap<>();
-	protected List<Chat>			chats		= new ArrayList<>();
-	protected IDGenerator			idGenerator;
-	protected CacheMap				cacheMap	= new CacheMap();
+	protected User				user;
+	protected Map<String, User>	users		= new HashMap<>();
+	protected List<Chat>		chats		= new ArrayList<>();
+	protected IDGenerator		idGenerator;
+	protected CacheMap			cacheMap	= new CacheMap();
+	protected Instant			lastSync	= Instant.EPOCH;
 
 	{
 		cacheMap.put(Message.class, new Cache<>());
@@ -42,10 +44,11 @@ public abstract class LocalDB {
 	 * Stores all users. If the client user is specified, their chats will be stored
 	 * as well. The message id generator will also be saved if present.
 	 *
+	 * @param isOnline determines which {@code lastSync} time stamp is saved
 	 * @throws Exception if the saving process failed
 	 * @since Envoy Client v0.3-alpha
 	 */
-	public void save() throws Exception {}
+	public void save(boolean isOnline) throws Exception {}
 
 	/**
 	 * Loads all user data.
@@ -77,7 +80,7 @@ public abstract class LocalDB {
 	 * @since Envoy Client v0.1-beta
 	 */
 	public void synchronize() {
-		user.getContacts().stream().filter(u -> u instanceof User && !users.containsKey(u.getName())).forEach(u -> users.put(u.getName(), u));
+		user.getContacts().stream().filter(u -> u instanceof User && !users.containsKey(u.getName())).forEach(u -> users.put(u.getName(), (User) u));
 		users.put(user.getName(), user);
 
 		// Synchronize user status data
@@ -98,7 +101,7 @@ public abstract class LocalDB {
 	 *         user names as keys
 	 * @since Envoy Client v0.2-alpha
 	 */
-	public Map<String, Contact> getUsers() { return users; }
+	public Map<String, User> getUsers() { return users; }
 
 	/**
 	 * @return all saved {@link Chat} objects that list the client user as the
@@ -148,6 +151,12 @@ public abstract class LocalDB {
 	 */
 	public CacheMap getCacheMap() { return cacheMap; }
 
+	/**
+	 * @return the time stamp when the database was last saved
+	 * @since Envoy Client v0.2-beta
+	 */
+	public Instant getLastSync() { return lastSync; }
+
 	/**
 	 * Searches for a message by ID.
 	 *

client/src/main/java/envoy/client/data/PersistentLocalDB.java

@@ -1,6 +1,7 @@
 package envoy.client.data;
 
 import java.io.*;
+import java.time.Instant;
 import java.util.ArrayList;
 import java.util.HashMap;
 
@@ -26,7 +27,7 @@ public final class PersistentLocalDB extends LocalDB {
 	/**
 	 * Constructs an empty local database. To serialize any user-specific data to
 	 * the file system, call {@link PersistentLocalDB#initializeUserStorage()} first
-	 * and then {@link PersistentLocalDB#save()}.
+	 * and then {@link PersistentLocalDB#save(boolean)}.
 	 *
 	 * @param dbDir the directory in which to persist data
 	 * @throws IOException if {@code dbDir} is a file (and not a directory)
@@ -57,12 +58,12 @@ public final class PersistentLocalDB extends LocalDB {
 	}
 
 	@Override
-	public void save() throws IOException {
+	public void save(boolean isOnline) throws IOException {
 		// Save users
 		SerializationUtils.write(usersFile, users);
 
-		// Save user data
-		if (user != null) SerializationUtils.write(userFile, chats, cacheMap);
+		// Save user data and last sync time stamp
+		if (user != null) SerializationUtils.write(userFile, chats, cacheMap, isOnline ? Instant.now() : lastSync);
 
 		// Save id generator
 		if (hasIDGenerator()) SerializationUtils.write(idGeneratorFile, idGenerator);
@@ -76,6 +77,7 @@ public final class PersistentLocalDB extends LocalDB {
 		try (var in = new ObjectInputStream(new FileInputStream(userFile))) {
 			chats		= (ArrayList<Chat>) in.readObject();
 			cacheMap	= (CacheMap) in.readObject();
+			lastSync	= (Instant) in.readObject();
 		}
 	}